It is conventional to determine the resistive state of a resistive memory cell, and thus the data bit stored in the resistive memory cell, by using an operational amplifier to compare a voltage dependent on the resistive state of the memory cell with a reference voltage obtained from a reference resistive memory cell. A reference memory cell is used to provide the reference voltage since it will be subjected to the same temperature and voltage influences as the cell being read and it will typically be affected by manufacturing tolerances in a manner similar to the cell being read.
A resistive memory cell has a resistance that can be programmed to have either a high resistance value or a low resistance value when accessed. One example of a conventional resistive memory cell is a PMC (programmable metallization cell), which utilizes electrochemical control of nanoscale quantities of a metal in thin films of solid electrolyte. A PMC can have a low resistance value of, for example, 104 ohms and a high resistance value of, for example, 109 ohms. The low resistance value can represent a data bit having a logic 1 value and the high resistance value can represent a data bit having a logic 0 value (or vice-versa). Another example of a conventional resistive memory cell is a phase change memory cell, which has a high resistance value in an amorphous state and a low resistance vale in a crystalline state. A heater element is used to heat a programmable volume of the phase change memory cell and to place the programmable volume into the amorphous state or the crystalline state.